Wavelength division multiplexed (WDM) optical communication systems (referred to as “WDM systems”) are systems in which multiple optical signals, each having a different wavelength, are combined onto a single optical fiber using an optical multiplexer circuit (referred to as a “multiplexer”). Such systems may include a transmitter circuit, such as a transmitter (Tx) photonic integrate circuit (PIC) having a transmitter component that includes a laser associated with each wavelength, a modulator configured to modulate the output of the laser, and a multiplexer to combine each of the modulated outputs (e.g., to form a combined output or WDM signal).
A WDM system may also include a receiver circuit having a receiver (Rx) PIC. The receiver PIC may include a polarization beam splitter (PBS) to receive an optical signal (e.g., a WDM signal), split the optical signal, and provide two optical signals associated with the received optical signal. The receiver PIC may also include an optical demultiplexer circuit (referred to as a “demultiplexer”) configured to receive the optical signals provided by the PBS and demultiplex each one of the optical signals into individual optical signals. Additionally, the receiver circuit may include receiver components to convert the individual optical signals into electrical signals, and output the data carried by those electrical signals.
The transmitter (Tx) and receiver (Rx) PICs, in an optical communication system, may support communications over a number of wavelength channels. For example, a pair of Tx/Rx PICs may support ten channels, each spaced by, for example, 200 GHz. The set of channels supported by the Tx and Rx PICs can be referred to as the channel grid for the PICs. Channel grids for Tx/Rx PICs may be aligned to standardized frequencies, such as those published by the Telecommunication Standardization Sector (ITU-T). The set of channels supported by the Tx and Rx PICs may be referred to as the ITU frequency grid for the Tx/Rx PICs.
A WDM signal may include channels susceptible to the Kerr effect. The Kerr effect is a change in the refractive index of a material in response to the intensity of the optical field. The Kerr effect may cause nonlinearities in a WDM signal which may lead to data loss and may prevent a receiver circuit from properly decoding the WDM signal. In an optical link where the dispersion stays near zero, such as in terrestrial dispersion managed links, or near the center of the repeater bandwidth in submarine links, the Kerr effect from neighboring channels, known as cross-phase modulation, is stronger than in terrestrial links that are not dispersion managed, or at the edges of the repeater bandwidth in submarine links.